The present invention relates generally to a method of treating wastewaters produced during industrial processing. More specifically, the present invention relates to a method of treating industrial wastewaters by employing a combination of peroxide and iron salts to pre-treat the wastewater prior to removing contaminant materials by filtration.
The treatment of wastewaters is a complex field. The complexities are due in part because the concentration and identity of the contaminant materials to be treated are constantly changing. Additionally, the flow rate, pH, oxidation potential, concentration of solids and temperature of the wastewater, among other factors, are also variable. Further, many wastewaters contain organic matter, including colloids, dissolved ionic matter, dissolved non-ionic matter, surfactants, and suspended solids. Such contaminant materials are present in combination with similar types of inorganic materials. Industrial wastewaters produced during industrial processing such as, electroplating, printed circuit manufacturing and machining, have proven difficult to treat due to the many different types of contaminants present in the wastewater. Despite these facts, filtration is a key part of most wastewater treatment plans. Many dissolved materials can be most easily removed if they are converted to an insoluble solid. Pre-existing solids removal is also usually necessary.
Filtration systems using many different types of filters have found wide use for the treatment of wastewaters. A common problem with such systems is the frequent need to clean or replace the filters due to fouling and clogging. Frequent filter cleaning is inefficient and wastes large amounts of chemicals. Frequent filter cleaning also requires the use of larger filtration apparatus to compensate for the downtime during cleaning. Frequent filter replacement is likewise wasteful of resources.
Many techniques have been employed by prior systems to address this problem. Sand filtration, using a graded series of layers of particles of different sizes and densities, is one example of a technique used to minimize backflushing and regeneration, while maintaining high filtration rates without the use of chemicals. However, sand filtration is most suited for potable and sanitary water facilities. Facilities which desire to recover or reuse treated water need a better method.
Cross-flow filtration methods are commonly used to reduce filter fouling. However, this type of filtration involves high pressures and high velocity flow rates. Only a fraction of the water is filtered at each pass across the filter membranes, so the process is energy inefficient.
Traditional bag filters clog easily and give reduced filtration flow rates after short periods of use. They are also difficult to effectively clean. Chemical treatments are often used to decrease filter loadings by precipitating the bulk of materials using organic or inorganic precipitating and flocculating materials. The solids are then largely allowed to settle and are removed by decantation or other means. The remaining liquid often contains many fine and/or colloidal particles, and must be subsequently filtered.
An improved method and system for providing high flow rate, single pass, flow-through filtration, has been developed as described in U.S. Pat. Nos. 5,871,648, 5,904,853 and 5,900,220, the disclosures of which are hereby incorporated by reference in their entirety. These systems uses a combination of organic and inorganic flocculating and precipitating agents to form large, nonsticky particles in the treated wastewater. The large particles form a loose, non-adherent layer on the surface of a filter element, which allow high flow rates through the particles. Cleaning is relatively simple by using a short period of water backflush. While these systems have provided an advance in the art, it is desirable to further improve the filtration process, and to provide a method that is suited for removing the many types of contaminant materials found in industrial wastewaters.
Accordingly, it is an object of the present invention to provide an improved method of treating industrial wastewaters. In particular, the inventors have unexpectedly found that a significant improvement in the prior art process can be effected by pre-treating a wastewater with a combination of an iron salts and peroxide, prior to forming particles which are then filtered. This inventive method provides a more effective treatment of the wastewater, and of significant advantage the method is suitable for a wide variety of contaminant materials. Further, the method of the present invention decreases the cleaning frequency of the filtration systems, maintains high filtration flow rates, and is simple to implement.
In general, the present invention provides a method for treating industrial wastewaters including one or more contaminant materials, characterized in that the industrial wastewaters to be filtered are pre-treated with a combination of iron salts and peroxide at a pH in the range of about 2 to 6 prior to filtration.
In another aspect, the present invention provides a method of treating industrial wastewaters, comprising the steps of: providing a wastewater containing one or more contaminant materials. Iron salts and peroxide are added to the wastewater. The pH of the wastewater is adjusted to a pH in the range of about 2 to 6, and the resultant reaction is allowed to occur for at least about ten minutes.
After the specified period of time has elapsed, precipitating and/or flocculating agents are added to the wastewater. The pH is now adjusted preferably to a pH of 7 or greater, and contaminant bearing particles (also referred to a floc or precipitate) are formed. The wastewater is then filtered to remove the contaminant bearing particles. The wastewater may be filtered by any number of prior art systems, and the present invention is particularly suited for practice with single pass flow-through filters, and most particularly suitable for high flow rate single pass flow-through filters. The pretreatment step according to the present invention prior to filtration minimizes clogging and the frequency between cleaning cycles, while maintaining high filtration flow rates. It has been found that by employing the pre-treatment step of the present invention, the precipitate that is subsequently formed is more easily filtered, which reduces or minimizes the fouling of the filter membrane. Thus, another aspect of the invention is a method for minimizing the fouling of filters in a wastewater filtration system which receives wastewater containing contaminant materials, characterized in that wastewater is pre-treated with a combination of iron salts and peroxide prior to filtering said contaminant materials from the wastewater.